1. Field of the Invention
This invention relates to conveyors having a plurality of endless chains arranged side-by-side and driven around parallel paths having upper and lower runs, the upper runs providing the support for articles being conveyed. The invention also relates to a composite conveyor composed of at least two such conveyors arranged end-to-end.
2. Description of the Prior Art
In conveyors of the above type conventionally the chains are composed of elements having rollers which run along a roller track at the upper run. At the turning points at the ends of the upper run, sprocket wheels engage the chain elements. The sprocket wheels of the several chains are arranged coaxially at each end of the conveyor and conventionally are mounted on a common shaft.
Such conveyors are frequently used in many fields, e.g. the steel industry. Carrier plates may be mounted across the chains. The rollers are often hardened because of the loads which occur. Short conveyors are usually driven by electric motors through reduction gearing and the sprocket wheels. Rotary drive naturally provides the advantage of smoothness, but this is limited, in dependence on the load, the speed and the number of teeth on the drive wheel, by the so-called polygon effect. This effect arises out of the polygonal construction of the sprocket wheel: as a link of the chain runs in and out of the wheel, the chain is accelerated and retarded, thus causing the speed to fluctuate. This uneven running brings about jerky speed variations, which in practice are at least to some extent cancelled out both by the elasticity of the chains and wheels and by angular speed fluctuations. Stretching in the whole of the chain caused by the forces produced and play can be considerable and is often taken up by means of a tensioning device.
Play occurs in the drive linkage between the electric motor and the load to be transported and, over the course of time, increases as a result of wear and of the plastic deformation of components. If no additional measures are taken the electric motor will first overcome any play in the drive linkage when the chain conveyor is started before the load begins to move. During this starting phase, the motor speed may become considerable, together with the associated kinetic energy. As soon as all the play has been taken up, this kinetic energy is converted into a shock on the load, which is undesirable when the load consists of a stack of tinplates or of other material which would be adversely affected by this shock.
Components such as rails, chain wheels, etc. which are prone to wear should desirably be fitted in such a way that they are easily changed, but this has not generally been a consideration in design. In some conventional designs, the chain wheels are made up of segments which can be changed without dismantling the chain.
Transferring the load between chain conveyors which are in line with one another is not simple, and for this reason, a long continuous conveyor, with associated problems, is often preferred.
Illustrative of the prior art are U.S. Pat. Nos. 2,769,522, 3,024,888, 3,116,824 and 3,918,574 and U.K. Pat. specification No. 214,173. U.S. Pat. Nos. 2,769,522 and 3,918,574 and U.K. Pat. No. 214,173 need not be discussed. U.S. Pat. No. 3,024,888 shows the two sets of sprocket wheels at the junction of two chain conveyors mounted on a common drive shaft, one set being keyed to the shaft so as to be driven while the other set is idling on the shaft. The shafts are supported in a frame, and carry the chains. Odd and even numbers of chains alternate along the composite conveyor. U.S. Pat. No. 3,116,824 illustrates a similar arrangement, though here each conveyor section has two chains. Adjacent frame portions carrying shafts supporting the chains are rigidly linked by plates carrying the drive shafts.